The present invention relates to a hydraulic damper for an electromechanical valve, and in particular to a hydraulic damper that can provide relatively soft seating of an engine valve on an engine valve seat.
With a conventional mechanical engine valve train system, the profile of the cam not only controls the valve opening and closing events, but it also decelerates the valve as it approaches either a fully open or fully closed position. This is especially important during valve closing, since it prevents the valve from pounding against its seat which can cause noise and adversely affect durability. One of the significant challenges with electromechanical valve actuation systems is to replicate this xe2x80x9csoft landingxe2x80x9d feature repeatably over all operating conditions and at low cost.
Prior to the present invention many electromechanical valves required feedback control systems with precision position sensors to control the closing of the valve. The feedback control systems utilized complex algorithms which were highly nonlinear. The systems also required a complex structure and in many instances had to be adaptive or have interactive learning control schemes to compensate for changes in the electromechanical valve characteristics over the lifetime and operating conditions of an engine.
It is desired to provide a hydraulic damper useful in electromechanical valves which does not require costly controllers or the utilization of position sensors for proper operation.
The present invention provides a hydraulic damper for electromechanical valves utilized in internal combustion engines. In a preferred embodiment, the present invention provides a damper with a main body and a hydraulic filled interior cavity. The main body has aligned openings intersecting the interior cavity. The aligned openings provide passage for a valve stem which is operatively associated with the valve body.
An outer piston is slidably mounted within the damper main body interior cavity. The outer piston has its own interior hydraulic filled cavity. The hydraulic filled cavity of the outer piston also has aligned openings for passage of the stem therethrough. An inner piston is connected with the valve stem within the outer piston cavity. The inner piston is slidably mounted within the outer piston interior cavity. When urged toward a position proximate to one of the outer piston""s aligned openings, the inner piston will move the outer piston resulting in a very high damping force and extra moving mass near the end of travel of the stem. This high damping portion provides a low valve stem velocity when the valve is going towards its seated closed position.
It is an advantage of the present invention to provide a hydraulic damper which provides very low valve speeds towards an extreme end of the valve""s movement towards closure.